SOLUTION: in still water, a boat averages 7 mph. it takes the same amount of time to travel 20 miles downstream, with the current, as 8 miles upstream, against the current. what is the rate

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Question 338451: in still water, a boat averages 7 mph. it takes the same amount of time to travel 20 miles downstream, with the current, as 8 miles upstream, against the current. what is the rate of the water's current?
Answer by ankor@dixie-net.com(22740) About Me  (Show Source):
You can put this solution on YOUR website!
in still water, a boat averages 7 mph.
it takes the same amount of time to travel 20 miles downstream, with the
current, as 8 miles upstream, against the current.
what is the rate of the water's current?
:
Let c = rate of the current
then
(7+c) = effective rate downstream
and
(7-c) = effective rate upstream
:
Write a time equation: time = dist/rate
:
Time downstr = time upstr
20%2F%287%2Bc%29 = 8%2F%287-c%29
Cross multiply
20(7-c) = 8(7+c)
140 - 20c = 56 + 8c
140 - 56 = 8c + 20c
84 = 28c
c = 84%2F28
c = 3 mph is the current rate
;
:
:
Check this by finding the times
20/10 = 2 hrs
8/4 = 2 hrs